I saw it mostly thus; Ferrovax and Odin/Vadderung are the two powers in the accords who could take on Mab and beat her down, but choose to play around. All the other powers are weaker, or, in Summer's case, a somewhat equal counterbalance. As such, despite being very different, they're treated as equals.
The reasons why Ferrovax plays around are a bit fuzzy, since it's apparently not because he likes humans, but maybe he's been pushing humans to make robots? Iron, Ferrum, is a sign of human technology. And a weakness of the overtly magical Fae. Meanwhile Odin is all about the secret knowledge of things beyond technology; death, magic/foresight, people, that sort of thing.